As an example of this kind of illumination devices, a fog lamp is known which accommodates a light source and a projection lens in a lamp chamber defined by a housing and a translucent cover. When light emitted from the light source passes through the projection lens, the light is subject to a predetermined light distribution control so as to form a predetermined light distribution pattern in front of the vehicle (see, e.g., International Publication No. WO 2014/012878 A1).